I've seen something like this featured on the TV before, recently(ish). Certainly in the last 12 onths it was on. If its the same place, which i believe it is, its due to the seasons affecting the freeze/thawing of vast amounts of water/ice. Every year the water level in these serene vallys rise by as much as 8ft (i think). Benches, pathways, shrubs and trees are all temporarily submerged for either a few weeks or a couple of months each year. People apparently flock from all around the world to go scooba-diving there, for obvious reasons. I've seen photo's of 'couples' sitting on a bench canoodling in scooby gear, apparently underwater.
Its awesome, i'd love to swim amongst all that. Its picture perfect, absolutely beautifull. Thanks for sharing Ian.